Revert "Announce alerts through SemanticsService on Windows"

ci/licenses_golden/licenses_flutter

@@ -3063,13 +3063,9 @@ FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_texture_regi
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_value.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_view.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/flutter_linux.h
-FILE: ../../../flutter/shell/platform/windows/accessibility_alert.cc
-FILE: ../../../flutter/shell/platform/windows/accessibility_alert.h
 FILE: ../../../flutter/shell/platform/windows/accessibility_bridge_delegate_windows.cc
 FILE: ../../../flutter/shell/platform/windows/accessibility_bridge_delegate_windows.h
 FILE: ../../../flutter/shell/platform/windows/accessibility_bridge_delegate_windows_unittests.cc
-FILE: ../../../flutter/shell/platform/windows/accessibility_root_node.cc
-FILE: ../../../flutter/shell/platform/windows/accessibility_root_node.h
 FILE: ../../../flutter/shell/platform/windows/angle_surface_manager.cc
 FILE: ../../../flutter/shell/platform/windows/angle_surface_manager.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/dart_project_unittests.cc

shell/platform/windows/BUILD.gn

@@ -38,12 +38,8 @@ source_set("flutter_windows_headers") {
 source_set("flutter_windows_source") {
   # Common Windows sources.
   sources = [
-    "accessibility_alert.cc",
-    "accessibility_alert.h",
     "accessibility_bridge_delegate_windows.cc",
     "accessibility_bridge_delegate_windows.h",
-    "accessibility_root_node.cc",
-    "accessibility_root_node.h",
     "angle_surface_manager.cc",
     "angle_surface_manager.h",
     "cursor_handler.cc",